Wheel alignment in a vehicle, expressed for example as toe-in and camber angle, is an important factor affecting the straight-line stability, cornering characteristics and steering characteristics of the vehicle. The toe-in aspect of wheel alignment will now be explained, on the basis of FIGS. 20A through 20C hereof.
Toe-in refers to inclining inward of the front part of a wheel 200 as shown in FIG. 20B, or the degree of that inclining inward, from the state shown in FIG. 20A wherein the wheel 200 points in the forward direction of the vehicle. This toe-in is generally obtained by statically measuring the inclination angle (this inclination angle is called the toe angle) θ of the wheel 200. An apparatus which uses this kind of measuring method is disclosed in, for example, Japanese Patent Publication No. HEI-3-26767, “Vehicle Wheel Inclination Angle Measuring Apparatus”. With this apparatus the wheel is sandwiched between detection plates, and toe-in and camber angle are measured by detecting displacements of these detection plates from reference positions with a plurality of sensors.
However, with the measuring method disclosed in Japanese Patent Publication No. HEI-3-26767, the inclination angles of the wheel are measured on a vehicle which has been completed on a production line, and because the measurement is carried out along with other checks at the end of the production line; the number of items to be checked is large and the flow of the line may be held up.
Also, it is necessary for the wheel to be positioned precisely in the measuring position between the two detection plates, and the measurement entails a lot of labor.
Furthermore, for example with a wheel fitted with a tire having raised letters formed on its side faces, when these raised parts are sandwiched between the two detection plates, an error arises in the wheel inclination angle measurement result, and the measurement accuracy suffers.
Moreover, with this inclination angle measuring apparatus, to sandwich the wheel with the two detection plates, respective stays for supporting each of these detection plates and a linkage mechanism for moving the detection plates in synchrony and so on are necessary, and there are a large number of parts and the apparatus itself is complicated.
And in FIG. 20B, depending on the manufacturing accuracy of a wheel hub to which the wheel 200 is attached and a wheel shaft rotatably supporting the wheel hub, when the wheel 200 is rotated, the wheel 200 may oscillate from left to right about the position at which it is inclined through the angle θ. These left and right oscillation angles will be written as +α and −α.
FIG. 20C is a graph showing change of the toe angle occurring when the wheel 200 is rotated. The vertical axis shows the toe angle T and the horizontal axis shows time t. According to this graph, the toe angle T changes sinusoidally with time t, and the maximum value of the toe angle T is θ+α and its minimum value is θ−α. So for example in FIG. 20B, if the inclination of the wheel 200 is measured statically with the wheel 200 inclined through an angle (θ+α) with respect to the vehicle forward direction, an error of angle α will arise.